Thermostatic switch



Feb. 28, 1933. K'CLARK 1,899,671

THERMOSTATIC SWITCH Filed July 18, 1930 INVENTOR Earl K Clarlf ATTORNEYPatented Feb. 28, 1933 UNITED STATES PATENT OFFICE EARL K. CLARK, OIIANBFIELD, OHIO, ASSIGNOR TO WETINGHOUSE ELECTRIC &

IANUFAGIUBING COKPANY, A CORPORATION OF PENNSYLVANIA TEE-RKOSTATICSWITCH Application filed July 18, 1880. Serial N0. 468,854.

. My invention relatesto thermal devices and particularly tothermostatic swltches.

An object of my invention is to provide a relatively simple and compactthermal devlce which shall cause a plurality of movements 'ofone contactmember relatively to a cooperating contact member.

Another object of my invention is to provide a relatively simple andinexpensive structure for the thermostatic control of heating elementswhich are to be operated at a plurality of different temperatures.

In practicing my invention, I provide a base member, of substantiallybar shape, a movable contact bar structure, of substantlally U-shape,and a pair of substantially coextensive and spaced bimetal bars toactuate the contact structure of U-shape in aplurality of predetermineddirections relatively to a fixed contact. member or members.

In the single sheet of drawings,

Figure 1 is a view, partially in side elevation and partially-insection, of a thermostatic switch assembly embodying my invention;

Fig. 2 is a view in end elevation thereof,

Fig. 3 is a top plan view of the device with the casing removed;

Fig. 4 is a view in side elevation with the cover shown in section of amodified form of device embodying m invention, and

' Fig. 5 is a view in en elevation thereof.

Referring more particularly to Figs. 1 to 3, inclusive, I have thereillustrated a metal base plate 11 which is provided with an mtermediateinwardly bent portion 12. The right-hand end portion of the basemember11 is provided with a recess 13 for receivmg therein aterminal-supporting member 14 of electric-insulating material. Aplurality of adjustable contact members 16, 17 and 18 extend through themember 14 and may be locked in any adjusted position by nuts 19 thereon.

' A contact spring member 21, of substantially U-shape, has oiie -endportion thereof secured to the base, as by rivets 22 at the portion 12of the base. A contact member 23 is secured to the other end of themember 21 closely adjacent to the end of the arm and in such position asto operatively engage contact terminal 16. A relatively thin metal plate24 has one of its ends riveted to an intermediate portion of the upperpart of the member 21 as by rivets 26. The other end of member 24 isslit so as to provide two arms 27 and 28, each of which arms areprovided with contact members 29 and 31, respectively, so located as tooperatively engage terminals 17 and 18.

A bimetallic strip 32 has one end thereof secured against the endportion of spring contact member 21 by the rivets 22 and extends towardthe intermediate portion of member 21 the free end thereof beingprovided with a nt-outportion 33 which operative-ly engages the springcontact member 21. A second bimetal strip 34 has one end thereof securedto a resilient suppor 36 in the shape of a bar which has one end thereofsecured by the rivets 22 to the intermediate portion 12. The other endof member 36 is suitably secured as by welding or by a rivet 37 to thesubstantially fixed end of bimetal bar 34. The other end of the bar 34is adapted to engage the upper portion of spring contact arm 21, butinitially there is a small clearance between the free end of the arm 34and more particularly between the bent-out portion 38 and the inner faceof arm 21, for a purpose to be hereinafter specified.

In order to permit of adjusting the switch assembly and thereby to varythe temperature at which the devicewill operate, a machine screw 41extends through one part of the base plate 11 adjacent to one end andthrough the members 21 and 32 and engages rivet 37 and may be locked inany position by a lock nut 42.

A casing 43, of substantially U-shape, fits over the edge portions ofbase plate 11.

51 terial. with a plurality of terminals 53, 54

and 56 extending therethrough and held by ldck nuts 57. The springcontact member of substantially U-shape is here made in two portionsincluding a portion 58 of substantially 1O U-shape and a bar 59 whichhas associated therewith a double arm contact element-61 as washereinbefore set forth for the arm 24 shown in Fig. 1 of the drawing.

A bimetal strip 62 has one end secured to the base 51 as by rivets 63and has its other end operatively engaging one leg portion of the member58. A second bimetal bar 64 has one end thereof secured to a springsupporting member 66, the other end of WhlCll is secured to the base 51by the rivets 63. The free end. of bimetal bar 62 is bent laterallyfirst in one direction and then in the reverse direction from the planeof the rest of the bar to constitute a pocket of V-shape to receive theend of portion 67 of the arm 59 in abutting relation, the arm 59 and themember 58 constituting, in effect, a spring contact member ofsubstantially U-shape.

A small machine screw 68 extends through the base 51 and throughopenings in member 58 and bimetal bar 62 into operative engagement withthe end of spring arm 66, in order to adjust the device, a nut 69 beingprovided on the screw 68 to lock it in any desired adjusted position. Acasing 71 of U-shape, is adapted to slidingly fit over the edge portionsof base member 51.

The device embodying my invention was designed particularly for use withWarming pads and one or more of these thermostatic switches may belocated in the warming pad so as to control the temperature thereof.

The heating element of a warming pad or, in fact, of any electricallyheated device, is represented by heating element 73 and a manuallyoperable switch 74 is provided having a movable contact arm which may bemoved selectively into engagement with fixed contact members 76, 77 or78. The contact members 76, 77 and 78 are connected, by suitableconductors, to the terminals 16, 17 and 18 or in the device shown inFig. 4 to terminals 53, 54 and 56.

Assuming that the device has been properly adjusted and that contact armof switch 74 is in engagement with contact member 76, I have found itpossible to maintain an average temperature in a warming pad on theorder of 120 F. If contact member 77 is engaged, I have found that anaverage temperature of 150 F. may be maintained, while, if contactmember 78 is engaged by the switch arm, an average temperature of 180 F.may be maintained. 1.

The movable contact structure, including As was hereinbefore stated, themovable end of bimetal bar 32 is in engagement with a part of springcontact member 21 before the free end of bar 34 is in engagementtherewith. Upon sufiicient change of temperature to cause movement ofthe bar 32, it will move downwardly or toward the base 11, so that v theupper portion of the arm 21 will, in effect, be moved toward the left,whereby a scraping action is effected between the cooperating fixed andmovable contact members. This, of course, will have the result ofcleaning the cooperating contacts without breaking or interrupting thecircuit. At a difierent predetermined temperature, the end 38 of bar 34will engage the spring contact member 21 and will cause. dis-engagementof contact members 23 and 16, then the dis-engagement of contact members29 and 17 and finally of contact members 31 and 18, it being assumed, ofcourse, that the temperature varies a suflicient amount to cause suchaction.

Upon the reverse changes of temperature, the reverse sequence ofoperation will be effected, that is, the cooperating contact memberswill be moved into engagement and then will be caused to scrape one uponthe other to efi'ect a cleaning of the contact members and, therefore,obtain a better engagement therebetween.

The device embodying my invention thus provides a means for effecting aplurality of movements in diiferent directions and in a predeterminedsequence in a thermostatic switch embodying a bimetal actuating element.Also the first bimetal bar effects movecontact members, so that anyradio devices.

operated in the neighborhood of a thermostat of this kind are notaflected to any appreciable extent.

Various modifications may be made in. the device embodying my inventionwithout departing from the spirit and scope thereof, and

I desire, therefore, that only such limitations shall be placed thereonas are imposed by the contact member on the base, a sprin contact bar onsaid base and a plurality o bimetal members on said base for actuatingthe spring contact bar in sequence in different directions at rightangles to each other relatively to the 10 fixed contact member.

2. In a thermostatic switch, a base, a fixed contact member on the base,a spring contact arm, of substantially U-shape, mounted on the base, anda plurality of bimetal bars located within the spring contact member andsupported by the base for actuating the spring contact arm in sequencein different directions at right angles to each other relative to thefixed contact member.

3. In a thermosatic switch, a base, a fixed contact member on the base,a spring contact member, of substantially U-shape, supported by saidbase, a first bimetal bar mounted on the base and having its free endengaging the spring contact member to eflect a scraping movement betweenthe engaged contact members and a second bimetal bar supported by saidbase and efiective to cause aseparating movement of'the contact members,upon a predeterminedchange of temperature. fi

4. In a thermostatic switch, a base, a contact member on the base, aspring contact member operatively supported on the base and spacedtherefrom, a bimetal strip having one end mounted on the strip and itsother end operatively engaging the spring contact members to effectscraping movement between the contact members, a second bimetal barhaving one end resiliently supported on said base and having its otherend engaging the spring contact member to cause separation of thecontact members upon a predetermined variation of temperature, and meansoperativel engaging the resilientlysupported end 0 the second bimetalbar to vary the temperature at which separation of the contact membersoccurs.

5. A thermostatic switch including a base, a plurality of fixed contactmembers on the base, a resilient bar providing a plurality of contactarms of different rigidity cooperating with the fixed contact membersand a plurality of bimetal bars on the base for actuat-ing the resilientbar in different directions at right angles to each other to effectdisengagement between the cooperating contact members in sequence and atdifferent temperatures. I

6. A thermostatic switch including a fixed contact, a spring contact armcooperating with the fixed contact and a pair of bimetal bars engagingthe spring contact arm, one of said bimetal bars effecting a scrapingmovement between the cooperating contact members and the second bimetalbar effecting se aration therebetween.

A thermostatic switch including a fixed contact, a spring contact armcooperatin with the fixed contact and a pair of bimeta bars engaging thespring contact arm at different points along its len h and effective toactuate it in sequence in di erent directions at right angles to eachother relatively to the fixed contact member.

In testimony whereof, I have hereunto subscribed my-name this 13 day ofJune, 1930. EARL K. CLARK.

